A solenoid actuator for operating hydraulic equipment such as a needle valve by performing a linear motion, drives a plunger using a magnetic force generated by a coil, thereby driving a shaft fixed to the plunger in an axial direction.
JPH11-031617A, published by the Japan Patent Office in 1999, proposes a guide tube made of a non-magnetic material to support the plunger so as to be free to slide. The guide tube is formed in a cylindrical shape having a bottom and the plunger is housed in the guide tube so as to be free to slide therein. A base made of a magnetic material is disposed in the interior of an opening of the guide tube. The guide tube is fitted into a hollow portion of a bobbin on which a coil is wound. When the coil is energized, a magnetic flux is formed between the coil and the base via the plunger such that the plunger is attracted towards the base.
The guide tube functions as a pressure vessel which prevents a pressure change in a plunger working chamber from being transferred to the bobbin on the outside. The guide tube thereby ensures pressure tightness in the solenoid actuator.